Ultra-high sensitivity silver halide color photographic light-sensitive materials have been strongly desired in recent years, which can be used in a room of insufficient illumination without any electric flash (strobe) or with a strobe of low light quantity, i.e., in a condition as natural as possible, or which can be used in a camera with a telephoto lens under conditions of high shutter speed and high aperture value to take, for example, sport pictures.
It is well known in the art that the sensitivity of silver halide light-sensitive materials can be increased by increasing the size of silver halide grains. However, as described in Farrell et al., J. Phot. Sci., 17 (1969), page 116 and ibid., 9 (1961), page 73, if the size of silver halide grains is increased beyond a certain limit, the efficiency of increasing sensitivity will drop. This is accompanied by undesirable problems, such as a serious reduction in sensitivity/grain size ratio, undesirably high production costs due to the significant amount of silver coated, and deterioration in processing properties, such as a reduction in fixability.
Another means to increase sensitivity is disclosed in, for example, U.S. Pat. Nos. 3,663,228, 3,849,138, 4,184,876 and 4,186,016. In accordance with this method, high-sensitivity blue-sensitive, green-sensitive and red-sensitive layers are placed more away from a support than low-sensitivity green-sensitive and red-sensitive layers and, if necessary, a low-sensitivity blue-sensitive layer. It has been found, however, that even if this method is employed, since the red-sensitive layer is positioned below blue-sensitive and green-sensitive layers, the loss of absorption of light, delay of development, and so forth occur, it impossible to realize ultra-high sensitivity.
It is also known that sensitivity can be increased by shortening the coupling speed of couplers. It has been found, however, that even if such high-coupling speed couplers are used in emulsions formulated to contain silver halide grains of large size for the purpose of increasing sensitivity, the sensitivity can be increased only insufficently, and a deterioration of graininess is undesirably involved.
Another method of increasing sensitivity is disclosed in U.S. Pat. No. 3,497,350, in which at the furthest position from a support is placed a light-sensitive emulsion layer which contains a black image-forming coupler or a combination of yellow image-forming coupler, magenta image-forming coupler and cyan image-forming coupler, and which is sensitized to red light and to green light. However, this method has been found also undesirable, since deterioration in color is involved.
Thus, it has been strongly desired to develop a satisfactory means to achieve high sensitization.